The present invention relates to a method and apparatus for analyzing a blood or other biological fluid sample in a quiescent state without the need for additional diluting reagents or fluid streams passing through the apparatus during the analytic process, whereby particulate constituents of biological samples can be enumerated and inspected using an optical scanning instrument. Specifically, this invention relates to a method and apparatus for obtaining decreased cellular or particulate concentrations within the use of this system.
The formation of appropriate cellular or particulate layers for later optical examination is important to many fields. One of these fields is hematology where several methods and devices have been described for obtaining clinically useful cell concentrations. The manual wedge smear yields results of acceptable accuracy when performed by a skilled clinician but is time consuming, expensive, and presents a biohazard risk. Instrumentation to perform a complete blood count, or xe2x80x9cCBCxe2x80x9d, may also be used but has significant disadvantages which are, for example, in the complexity of operation, potential leak failures, low system reliability, and higher maintenance costs.
Cellular analysis by capillary volumetric scanning, for example, in U.S. Pat. Nos. 5,547,849 and 5,585,246, describes another method for obtaining several CBC parameters whereby controlled cell layers are obtained for optical scanning. However, it cannot measure cell morphology and red blood cell parameters. U.S. Pat. No. 4,790,640 discloses a device for separating certain selected cells by capturing them in a wedge shaped geometry, but the disadvantage of this device is that the resulting separation of cells are packed together making optical examination of individual cells difficult.
In pending U.S. Ser. Nos. 09/248,135 and 09/249,721, a method and apparatus for analyzing a blood or other biologic fluid sample in a quiescent state without the need for separate fluid streams passing through the blood sample during the analysis is described. Although this method simplifies the analysis procedure and yields the full complement of CBC parameters, it also possesses several disadvantages. One disadvantage of this apparatus is that the concentration of cells in the examination layer is not controlled except through chamber height which can lead to difficulties in optically examining cell volume and morphology. Another disadvantage of the aforementioned apparatus is that the field of cells may be too sparse in clinically relevant samples for scanning to be completed in a timely manner.
U.S. Pat. No. 4,022,521 describes a transparent specimen slide having precision projections on one side for accurate control of the specimen thickness allowing viewing of a monolayer of blood cells. A disadvantage of this apparatus is that it does not provide for control of the density of cells in the viewing area making optical identification of cellular species difficult. Another disadvantage of this apparatus is that the device is free to float, thereby allowing inaccuracies in defining the gap thickness and making volumetric measurement difficult.
It would therefore be desirable to have a better controlled and more reliable method and apparatus for obtaining the desired cellular concentrations in a blood or, other biologic sample without the need for a separate dilution step and addition of diluting fluids, as set forth in the present invention.
It is an objective of the present invention to provide separation-channels within a sample chamber having sufficient size and dimensions to allow a desired particle species to pass while excluding others, thereby arriving at a predetermined relative volume fraction of the desired particle.
It is another objective of the present invention to incorporate two or more channel sizes selected to allow one or more cell types of interest and the substantially liquid component of the sample to pass through them arriving at desired cell concentrations.
It is a further objective of the present invention to define the distance between adjoining parallel channels, or their dimensional pitch, and channel dimensions to effect the desired volume fraction of cells or particles of interest in the specimen.
It is also an objective of the present invention to regulate the volume fraction of cellular or particle components of a specimen by means of an array of channels which effect their selection by means of size exclusion during flow between two adjoining compartments.
It is an additional objective of the present invention to create regions of individual red blood cells (RBCs) or other particles and regions of red blood cell Rouleaux suitable for volumetric measurement of individual RBCs and hematocrit, respectively.
It is a further objective of the present invention to re-combine the fluid and particles, without introducing air bubbles into the specimen within the subsequent chamber.
It is yet a further objective of the present invention to guarantee an accurate spacing between two opposing containment walls to allow for the optimal formation of desired cellular regions and an accurate determination of the chamber thickness without relying on extraneous equipment and manipulations for height calibration.
It is another objective of the present invention to control the advance of a fluid meniscus during filling of the chamber by means of notches located in one containment wall of the chamber oriented substantially perpendicular to the advancing meniscus.
It is yet another objective of the present invention to stop the flow of fluid and contain its volume in the chamber while allowing for free passage and venting of air by means of a wall surrounding the chamber which contains a multiplicity of venting-channels interspersed along it and a moat surrounding the wall and fill channels.